There is only one way to remove or delete the default wallpaper on your Samsung Galaxy Android phone: blank 1 pixel PNG file.

Yeah, it's just a simple 123 bytes image.

Here's the step by step instructions:

1. Create a black 1×1px image manually or just download it from here
2. Save it in your phone gallery
3. Open the gallery and find that image
4. Tap on «...» or look for some submenu with «Set as wallpaper» title
5. Ignore the warning about image size
6. Be happy with you beautiful black background with no wallpaper at all

In the end you can remove image from gallery. The background will stay black.